Exploring, drilling, completing, and operating hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. In recognition of these expenses, added emphasis has been placed on well access, monitoring and management throughout its productive life. Ready access to well information as well as well intervention may play critical roles in maximizing the life of the well and total hydrocarbon recovery. As a result, downhole tools are frequently deployed within a given hydrocarbon well throughout its life. These tools may include logging tools to provide well condition information. Alternatively, these tools may include devices for stimulating hydrocarbon flow, removing debris or scale, or addressing a host of other well issues.
The above noted downhole tools are generally delivered to a downhole location by way of a well access line, often a wireline cable. Once positioned downhole at the end of the well access line a well application may be employed by such a tool. A winch at the surface of the oilfield may then be employed to withdraw the well access line and tool from the well. However, in many cases the tool may be stuck in place downhole. This may be due to the presence of an unforeseen obstruction, unaccounted for restriction, differential sticking of the tool against the well wall, a malfunctioning tractor, or a host of other reasons. Indeed, with the presence of increasingly deeper and more deviated wells, the likelihood of a downhole tool becoming stuck merely due to the depth and architecture of the well alone is increased.
Regardless of the particular reason for the sticking of the downhole tool, continued withdrawal of the well access line by the winch may lead to significant line or tool damage. Furthermore, continued driving of the winch is likely to result in breaking of the well access line, leaving potentially several thousand feet of line in the well if preventable measures aren't taken. Thus, in order to help avoid a circumstance in which the well access line is broken, a release mechanism is generally incorporated into the logging head which serves as the connection between the downhole tool and the well access line. In this manner, the winch may continue to pull the line out of the well, leaving only the downhole tool and part of the logging head behind. A subsequent fishing application may take place in order to retrieve the tool and logging head remains.
One type of release mechanism involves using a separable housing that is held together by at least one tensile stud. The housing makes up the body of the logging head which may be broken once a predetermined load is applied to the tensile stud thereof. Often this is referred to as incorporating a “weakpoint” into the logging head through the use of the tensile stud. For example, consider a tensile stud providing a weakpoint of about a 2,000 lb. threshold to a logging head coupled to a tool stuck in the well. In such a case, the logging head will break, freeing the well access line from the well once the pull of the winch exceeds about 2,000 lbs.
Unfortunately, employing a tensile stud incorporated into the housing of the logging head requires that the tensile stud and load threshold be predetermined. That is, the most effective size of the threshold to be incorporated into the logging head may be dependent on a variety of factors. For example, the load threshold of the well access line itself, the potential sticking depth of the tool, and the overall size of the downhole toolstring may all play a role in determining the most effective tensile stud to use. As a practical matter, this means that a couple of different logging heads and between about 10 and 20 different tensile studs of different load thresholds, or “weakpoint” values, are generally made available at the oilfield. In spite of this large amount of equipment, only one of the tensile stud/head combinations are ultimately incorporated into the overall line assembly.
Often times, in an effort to minimize the amount of equipment brought to the site, an operator will bring fewer tensile studs to the site leaving fewer weakpoint values available. However, this runs the risk that the proper logging head will be unavailable on site adding significant delay to the operation or worse, the employment of an improper logging head of potentially catastrophic consequences. At a minimum, the operator is left with the option of hauling a significant number of unutilized studs to the site or risk the possibility of hundreds of thousands of dollars in lost time for failure to do so.
Alternative types of release mechanisms are often employed where the load threshold of the tensile stud would need to be fairly minimal in order to be effective. So, for example, where 15,000 lbs. of line are disposed within the well and the line has a load threshold of 16,000 lbs., this effectively leaves the possibility of employing a tensile stud of less than a 1,000 lb. threshold. Thus, rather than employ such a minimal tensile stud, a remote release mechanism such as an explosive charge or an electrically actuated mechanism positioned at the logging head may be used to free the wireline from a tool stuck downhole.
Unfortunately, employing an explosive charge for use with a logging head release mechanism comes with the inherent risks associated with the use of explosives for any purpose. That is, operator safety has potentially been compromised due to the possibility of accidental discharge. On the other hand, providing electrical power downhole may be a significant challenge. For example, conventional techniques for electrically actuating a release mechanism require several amps of power. As a result, where an electrical release mechanism is employed, electrical cable is generally added onto the well access line in order to meet the power requirements. Given that the well is likely of significant depth, this means that a considerable amount of weight has been added to the line in order to employ such a release mechanism. As such, the overall effectiveness of the operation itself may be compromised.